Defacement in the Chapel!

Art is to be appreciated from afar, rarely touched, and certainly never altered from the artist's original vision. One would never pencil in eyebrows on the Mona Lisa or dare to bolt mannequin arms to the Venus de Milo.

Yet, despite all this, there is a well-known piece of art that has been blatantly defaced. What is even stranger is that the offending defacer, though he meant to do his nasty work, did not WANT to. His identity was known, yet he was never arrested and never punished. Quite the opposite, his defacement was encouraged by the highest of powers in his day.